Orthogonal Frequency Division Multiplexing (OFDM) is a technique in which data is simultaneously transmitted over multiple sub-carriers separated (in frequency) by a multiple of the inverse of the symbol period. Due to the long symbol period, any frequency selective channel appears to be a flat channel which could be compensated by using a single frequency domain equalizer (FEQ) instead of using a complex time domain equalizer or multi-tap frequency domain equalizer. OFDM relies on the properties of the Inverse Fast Fourier Transform (IFFT)/Fast Fourier Transform (FFT) and orthogonality between the sub-carriers to achieve a 1 tap FEQ. Inter symbol interference (ISI) and Inter Carrier Interference (ICI) are two common factors which destroy orthogonality between the sub-carriers. Guard times (of durations equal to or greater than the maximum channel delay spread) are inserted between consecutive OFDM symbols to avoid ISI. The guard times may be in the form of some part of the end of the OFDM symbol which is added as a prefix to the OFDM symbol (commonly referred to as a cyclic prefix) or as zeros which are appended to the OFDM symbol (commonly referred to as a zero suffix). The length of the cyclic prefix or zero suffix is normally a fraction of the total OFDM symbol length. At the receiver, in a system employing a cyclic prefix, the prefix is discarded and the rest of the OFDM symbol is processed whereas in a system employing a zero suffix, the suffix samples are added to the beginning of the OFDM symbol in order to preserve the orthogonality between the sub-carriers. Suffix addition is a technique that may be employed in orthogonal frequency division multiplexing (OFDM) communication systems. Zero suffix addition has been suggested in connection with Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) systems. Using OFDM symbols, MB-OFDM systems implement Ultra Wideband (UWB) wireless communication under the regulations recently propagated by the Federal Communications Commission (FCC).
As stated above, separating transmitted OFDM symbols with a zero suffix helps to deal with potential multipath problems (such as ISI). At the receiver, a signal received during a zero suffix period may be added to a signal received during the preceding OFDM symbol period to simplify the demodulation implementation at the receiver (i.e., 1 tap FEQ). However, this addition process tends to add noise to the resulting summed signal that is further processed by the receiver. The zero suffix length is designed to accommodate the worst case multipath channel so that all the energy is captured and hence used in the demodulation of the signal. However, not all channels exhibit such strong multipath (e.g., AWGN channel which exhibits no multipath at all) and adding the entire zero suffix adds noise in the system with no added benefit. An improved method of processing received signals which are transmitted with a zero suffix would be useful.